Continuous Change of Second-order Nonlinear Optical Activity in a Cyano-bridged Coordination Polymer

Abstract

In this work, we continuously control the second-order nonlinear optical activity by tuning the piezoelectric property in a series of rubidium manganese hexacyanoferrates, RbIxMnII[FeIII(CN)6](x+2)/3·zH2O. Above x = 0.7, second harmonic generation (SHG) is observed, and the SH light intensity (ISH) gradually increases with increasing x. The crystal structures of this series are analyzed using Rietveld analysis and the maximum entropy method. The crystal structural data shows that the difference between the existing probability of the Rb ion in interstitial site-1 (PRb1) and site-2 (PRb2), PRb1 − PRb2, gradually increases with increasing x. Because the difference between PRb1 and PRb2 produces a 4̅ rotoinversion, the PRb1 − PRb2 value is considered to be related to the magnitude of piezoelectricity or SH susceptibility (χSH). From the analysis of the χSH tensors elements, the observed x dependence of ISH can be explained by the PRb1 − PRb2 value. Such a tunable system of second-order nonlinear optical activity is very rare in condensed matters.